1. Technical Field
The present invention relates to a bias circuit for supplying a bias current to a base of an operating transistor.
2. Background Art
Heretofore, a differential amplifier or the like has a pair of differential transistors Q51 and Q52 with emitters connected in common as shown in FIG. 4 and connected to a constant current circuit. Then, the differential transistors Q51 and Q52 input a signal and are supplied with bias currents from a bias circuit to enable an operation in accordance with the input signal.
FIG. 4 includes a power supply V51 and resistors R51 and R52, where an output voltage of the power supply V51 is supplied as a bias voltage via the resistors R51 and R52 to bases of the differential transistors Q51 and Q52.
However, bipolar transistors have temperature dependent parameters, such as base-emitter voltage VBE and DC current gain hFE. Therefore, when the bias circuit shown in FIG. 4 is used, the emitter voltages of the differential transistors Q51 and Q52 are temperature dependent.    Patent Document 1: Japanese Patent Laid-Open Publication No. Hei 8-340224
When operating an application with a relatively narrow dynamic range (D-range) over a wide temperature range, such as a mixer circuit or a circuit where low voltage operation is required, it is necessary to ensure dynamic range with temperature-independent operating points (emitter, collector voltages).